1. Field of the Invention
The present invention relates to a small-sized direct current switch which is appropriate for use in a portable electric drill or any other electric-powered tool, and particularly to such a small-sized direct current switch which requires the quick turning-off and slow turning-on.
2. Related Arts
If an electric-powered tool is loaded heavily, and if its direct current switch turns off slowly, the electric arc will appear an elongated length of time between the stationary and movable contacts of the circuit, thus causing the contacts to be melted in short time.
It is liable that the movable and stationary contacts are melted together as a whole, thus allowing the drill or cutter to continue to rotate in dangerous condition. To prevent such danger, it is necessary that the switch be made to turn off quickly, thereby suppressing the appearance of arc between the movable and stationary contacts.
If the switch is so designed that the movable contact may leave the stationary contact quickly in the instant of switching off, the movable contact will be driven toward the stationary contact at such an increased speed that the so accelerated movable contact may bounce repeatedly on the stationary contact in the instant of switching on. This will cause electric arcs to appear an elongated length of time between the movable and stationary contacts, thus expediting the wear and deformation of the movable and stationary contacts.
In an attempt to obviate such problem, it has been proposed that dielectric current switches be designed so as to be capable of switching off quickly and switching on slowly, so that the life of the switch may extend.
Referring to FIG. 12, in such a conventional seesaw type of dielectric current switch a common pointed terminal 1 has its ridge 1a as a fulcrum for supporting the seesaw-like plate 3, which has movable contacts 3a and 3b formed on its opposite ends. An actuator 4 has a pusher 5 spring-biased toward the ridge of fulcrum 1a. The pusher 5 is pushed against the seesaw-like plate 3, still allowing the actuator 4 to move the pusher 5 back and forth on the seesaw-like plate 3. Two stationary contacts 2a and 2b are formed in confronting relation with the movable contacts 3a and 3b. One of the stationary contacts requires no anti-bounce means, and is hereinafter referred to as xe2x80x9cpseudoxe2x80x9d stationary contact 2b. Likewise, the counter movable contact is referred to as xe2x80x9cpseudoxe2x80x9d movable contact 3b. The actuator 4 has anti-bounce projection 6 formed on the side of the pseudo stationary and movable contacts 2b and 3b. The anti-bounce projection 6 permits the movable contact 3a to move toward the stationary contact 2a at a reduced speed.
Assume that the actuator 4 is moved back and forth, allowing the pusher 5 to move back and forth on the seesaw-like plate 3. When the pusher 5 stands upright on the ridge of fulcrum 1a of the common terminal 1, the seesaw-like plate 3 is balanced in the middle, and when the pusher 5 is on either side of the ridge of fulcrum 1a, the seesaw-like plate 3 is tilted accordingly so that the movable contact on the descending end may be put in contact with the counter stationary contact.
Assume that the pusher 5 traverses the ridge of fulcrum 1a from the left to right side, and that the seesaw-like plate 3 turns clockwise. Then, the seesaw-like plate 3 abuts on the anti-bounce projection 6 of the actuator 4 to retard its quick turn. Specifically in spite of traversing the ridge of fulcrum 1a of the common terminal 1 the pusher 4 cannot continue to turn the seesaw-like plate 3 still more.
The manual drive of the actuator 4 subsequent to abutment of the anti-bounce projection 6 against the seesaw-like plate 3 will displace the anti-bounce projection 6 rightward, so that the anti-bounce projection 6 may leave apart from the seesaw-like plate 3. After the distance between the movable and stationary contacts 3a and 2a has been shortened, the movable contact 3a is driven and put on the stationary contact by the pusher 5 alone, requiring no manual push any more. Thus, the bounce can be eliminated.
Conversely assume that the pusher 5 traverses the ridge of fulcrum 1a from the right to left side, starting from the right end at which the movable contact 3a stays on the stationary contact 2a, and that the seesaw-like plate 3 starts turning counter-clockwise. Just prior to the pusher""s traversing the ridge of fulcrum 1a the anti-bounce projection 6 abuts on the seesaw-like plate 3. Thereafter, the force of the anti-bounce projection 6 to push down and turn the seesaw-like plate 3 counterclockwise about the ridge of fulcrum 1a increases so that it may be stronger than the pushing force of the pusher, thus forcedly departing the movable contact 3a from the stationary contact 2a even though they are melted and stacked together. After the pusher 5 traverses the ridge of fulcrum 1a, the movable contact 3a may be put apart from the stationary contact 2a by the pusher 5 alone.
FIG. 13 shows another conventional fast switching-off type of direct current switch. As shown in the drawing, a common terminal 9 has its pointed end 9a as a fulcrum for supporting the seesaw-like plate 8, which has movable contacts 8a and 8b formed on its opposite ends. An actuator 11 has a pusher 12 loosely fitted in its recess. The pusher 12 is pushed downward with a spring 10 in the recess of the actuator 11 so that it may be raised and lowered in the recess, still remaining on the seesaw-like plate 8 while the actuator 11 moves horizontally. Thus, the seesaw-like plate 8 is allowed to turn clockwise or counter clockwise about its fulcrum. The seesaw-like plate 8 has a plateau 13 lying from the fulcrum 9a toward the right movable contact 8a. 
When the actuator 11 is pushed rightward by hand, the pusher 12 is moved rightward on the seesaw-like plate 8, and it climes the plateau 13, continuing to move rightward while turning the seesaw-like plate 8 clockwise about its pointed fulcrum 9a. Finally the movable contact 8a abuts on the stationary contact 7a, making an electric connection between the common terminal 9 and the stationary contact 7a. 
The climbing-up of the plateau 13 effectively retards the abutment of the movable contact 8a on the stationary contact 7a, thus attaining the slow switching-on of the seesaw type of switch.
Conversely when the actuator 11 is pushed leftward, the pusher 12 slides down quickly from the plateau 13 when traversing the fulcrum point 9a, thus allowing the seesaw-like plate 8 to turn counter-clockwise about the fulcrum point 9a. Then, the spring 10 is allowed to extend the stepwise-distance or flight of the plateau 13 from the compressed condition in which the coil 10 was compressed by the pusher 12 remaining on the plateau 13. The sliding-own of the pusher 12 is expedited by the releasing of the spring 12 to give a quick push to the seesaw-like plate 8, thus attaining the quick switching-off of the seesaw-like switch.
As for the seesaw-like switch of FIG. 12, the switching-on can be satisfactorily retarded by the anti-bounce projection 6. The beginning of the switching-off, however, depends on the manual movement of the anti-bounce projection 6, and therefore, the switching-off is retarded, and is slower than that performed by the automatic seesaw action.
As for the seesaw-like switch of FIG. 13, disadvantageously the slowness in the retarded switching-on and the quickness in the expedited switching-off depend on the speed at which the actuator 11 is moved, and the bounce cannot be effectively prevented.
One object of the present invention is to provide a direct current seesaw type of switch which is capable of effectively expediting the switching-off and retarding the switching-on of the switch.
To attain this object, a direct current switch comprises an insulating housing, an actuator slidably fixed to the housing, a support fixed to the housing, one stationary contact and one pseudo stationary contact both fixed to the housing, the stationary and pseudo stationary contacts being arranged symmetrically with respect to the support, a seesaw-like plate having one movable contact and one pseudo movable contact fixed to its opposite ends, the seesaw-like plate being supported by the support to be balanced in the middle, and a swingable pusher operatively connected to the actuator to apply a pushing force to the seesaw-like plate all the time, is improved according to the present invention in that the seesaw-like plate has an engagement piece fixed thereto in the vicinity of the movable contact, and that the actuator has a resilient catch-and-hold piece fixed thereto on the movable contact""s side, whereby while the actuator is on the way to the end, the resilient catch-and-hold piece may catch and hold the engagement piece until the pusher makes the seesaw-like plate to be inclined toward the stationary contact, making the resilient catch-and-hold piece forcedly release the engagement piece, allowing the movable contact to quickly abut on the stationary contact.
The movable contact may be allowed to move toward the stationary contact after the swingable pusher traverses the support.
The engagement piece may comprise an inverted xe2x80x9cLxe2x80x9d-shaped piece whose upright leg is bent so as to be caught by the catch-and-hold piece.
The catch-and-hold piece may be of a spring plate.
The catch-and-hold piece may comprise an inverted xe2x80x9cUxe2x80x9d-shaped piece to pinch the engagement piece.
The catch-and-hold piece may be so shaped that it may push the engagement piece on one side.
The catch-and-hold piece may comprise an inverted xe2x80x9cUxe2x80x9d-shaped piece, and the engagement piece comprises a xe2x80x9cUxe2x80x9d-shaped piece, which is sized so as to be snugly fitted in the inverted xe2x80x9cUxe2x80x9d-shaped piece.
The seesaw-like plate may have a ramp formed in the vicinity of the fulcrum at which the support bears the seesaw-like plate, and the pusher and the actuator may be so loosely connected that the pusher may be allowed to swing while pushing the seesaw-like plate.
Other objects and advantages of the present invention will be understood from the following description of seesaw type of switches according to preferred embodiments of the present invention, which are shown in accompanying drawings.